Capacitor unit



May 15, 1956 FOSTER 2,745,993

CAPACITOR UNIT Filed March 20, 1953 I5 Sheets-Sheet 1 INVENTOR J. H. FOSTER CAPACITOR UNIT May 15, 1956 3 Sheets-Sheet 2 Filed March 20, 1953 Fla/7 R O T N E V m FIGJ ATTORNEY 3 Sheets-Sheet 3 J. H. FOSTER CAPACITOR UNIT May 15, 1956 Filed March 20, 1953 INVENTOR ATTORNEY FIG-Z3 United States Patent CAPACITOR UNIT James H. Foster, Erie,Pa., assignor to Eric Resistor Corporation, Erie, 'Pa., a corpora'tion of Pennsylvania Application March 20, 1953, Serial No. 343,658 1 Claim. (Cl. 317--249) This invention is intended to produce air dielectric capacitor units in which one or more of the electrodes are embossed or depressed a controlled distance below the surface of supporting plates of insulating material.

By stacking two of the plates with the electrodes carrying faces in contact with each other an air dielectric capacitor is obtained where the electrode spacing is determined by the depth to which the electrodes are embossed. As an alternative one of the electrode carrying plates may be used in conjunction with a metal plate in contact with the electrode carrying face. The construction is adapted to fixed and variable capacitors. Inductance elements can be built in to the capacitors to provide tuned circuits.

In the accompanying drawings :Fig. 1 is a sectional elevation of a trimmer condenser, Fig. 2-is a plan view of the rotor, Fig. 3 is a section on line 3-3 of Fig. 2. Fig. 4a is a diagrammatic view of a molding press for making the rotor, Fig. 4 is an enlarged fragmentary section through a portion of the rotor as it comes from the molding press, Fig. 5 is a view similar to Fig. 4 after the unembossed portions of the copper foil havebeen removed, Fig. 6 is a plan view of the stator of the Fig. l trimmer, Fig. 7 is a section on line 7-7 of Fig. 6, Fig. 8 is a plan view of a metal plate which can be substituted for the Fig. 6 stator, Pig. 9 is a plan view of a stator which includes inductive sections so that when the stator is assembled with a rotor a tuned unit is provided, Fig. 10 is a section on line 10-10 of Fig. 9, Fig. 11 is a plan view of a metal plate which is alternatively usable with the stator of. Pig. 9, Fig. 12 is a top plan view of a fixed condenser in which one of the electrodes is a metal plate and the other electrodes are metal foil embossed a controlled depth below the surface of a plate of insulation material, Fig. 13 is a section on line 13-13 of Fig. 12, Fig. 14 is a plan view of a stator to be mounted in stacked relation so as to provide a variable tuning condenser, Fig. 15 is a section on line 15-45 of Fig. 14, Fig. 16 is a plan view of a rotor unit the plurality of which are to be ganged together with the Fig. 14 stator units to provide the variable tuning condenser, Fig. 17 is a section on line 1717 of Fig. 16, Fig. 18 is a sectional elevation of the variable tuning condenser utilizing the Fig. 14 stator units and Fig. 16 rotor units, Fig. 19 is a modification of the stator unit, Fig. 20 is a section on line 20-24} of Fig. 19, Fig. 21 is a modification of the rotor unit, Fig. 22 is a section on line 22-22 of Fig. 21 and Fig. 23 is a sectional elevation of a variable condenser having the Fig. 19 and Fig. 21 units.

The trimmer condenser shown in Figs. 1 to 7 inclusive has two flat disks, 1 and 2, of insulating material arranged in face to face contact. The disk 1 is the rotor of the condenser and the disk 2 is the stator. The rotor is keyed to a pin 3 journaled in the stator 2 and secured in place by a snap ring 4. The pin has a screw driver slot 5 to facilitate adjustment. While the pin 3 keeps the rotor and stator in alignment, further alignment may be provided by an arcuate groove 6 in the rotor which receives an arcuate tongue 7 on the stator. The arcuate tongue and groove elements 6 and 7 accurately center the rotor 2,745,993 Patented May 15, 1956 and stator. The tongue and groove elements are merely concentric guide bearing surfaces and the centering effect is not limited to tongue and groove surfaces.

On the face 8 of the rotor which rides on the face 9 of the stator there is an electrode 10 which is depressed a controlled distance below the face 8 and can be made by the technique illustrated in Figs. 4a, 4, and 5. Since the accuracy of the capacity depends upon the electrode spacing, it is important that the position of the electrode 10 with relation to the surface or face 8 be accurately controlled. This can be done by the embossing technique illustrated in Figs. 4a, 4, and 5.

In Fig. 40, ii and 12 indicate dies of a plastic molding press. 13 indicates a blank of deformable plastic which may for example consist of felt like paper fibers impregnated with uncured or semi-cured phenolic resin. Other fibers and other resins may be used, the important characteristic being that the plastic is deformable under emboss ing or molding pressure. 611 the upper face of the sheet 13 which is to be electroded is placed a sheet 14 of adhesive and a sheet 15 of copper foil. The adhesive 14 may be precoated on the undersurface of the foil 15' or if the plastic in the sheet 13 has the property of wetting and adhering to the foil no adhesive may be necessary. The upper die 12 has a projection 16 of the same shape as the electrode 1d to be embossed into the upper surface of the rotor. it is important that the projection 16 have sharp corners 17 so that when the dies 11 and 12 are pressed together, the projection 16 on the die 12 will punch or stamp a section of foil having the shape of the electrode 10 out of the foil sheet is. The upper die 12 also has an arcuate rib which forms the groove 6 in the finished rotor. The dies 11 and are usually heated and are pressed together under a pressure SUffiCifiHt to emboss the electrode It; below the upper surface of the rotor and to set or cure the rotor to its final molded condition. When the molding operation is completed, the portion of the foil 15 which is to form the electrode 10 will be embossed below the upper surface of the rotor 1 a definitely controlled distance determined by the height of the projection 16 in the mold 12. This depth of embossing can be made very accurate. Outside of the electrode it} there will be other foil sections 19 which will rest on top of the upper surface of the rotor 1. These sections 19 which may be termed to be unembossed portions of the foil 15 are removed by a cutting or abrading operation which results in the finished piece shown in Fig. 5. During this cutting or abrading operation the upper surface of the part as it leaves the press shown in Fig. 4a is cut away to a depth below the unembossed portions 19 of the foil but not to the upper surface of the embossed portion 16 which is to form the rotor electrode. The surface cutting or abrading can be very accurately carried out so that the result is a finished rotor 1 where the electrode 10 is embossed a slight distance below the surface 8 of the rotor. The depth of embossing of the electrode Ill below the rotor surface 8 can be as little as a few thousandths of an inch.

Instead of stamping out the electrode from a larger sheet of foil during the embossing operation, it is obvious that a previously stamped metal piece of the same shape as the mold projection 26 will be embossed by the projection 16 to a controlled depth below the upper surface of the rotor determined by the height of the projection 16.

By appropriate changes in the dies, the stator illustrated in Figs. 6 and 7 can be made by the same technique illustrated in Figs. 4a, 4, and 5. In the finished stator there will be pair of electrodes 20 and 21 respectively provided with a lead 22 and 23. The electrodes 20 and 21 and the leads 22 and 23 are embossed a controlled distance below the upper surface 9 of the stator. In the case of the leads 22 and 23 these are also of course embossed below the depth of the arcuate ribs 7 which project above the stator surface 9. In order to minimize the capacity between the electrodes 20 and 21 thestator has a slot 24 which introduces an air gap between the electrodes thereby minimizing the interelec= trode capacity.

When the rotor 1 and stator 2 are assembled, the lower surface 8 of the rotor is in face to face engagement with the upper surface 9 of the stator. By turning the rotor relative to the stator the capacity can be varied. In the maximum capacity position, the electrode on the rotor registers with the electrodes and 21 on the stator. When the rotor is turned 90 from the maximum capacity position so that the electrode 1%) is at right angles to the electrodes 20 and 21 or in line with the slot 24- the capacity is a minimum.

In the construction illustrated in Figs. 1 to 7, both the electrode 10 on the rotor and the electrodes 26 and 21 on the stator are embossed below the surfaces of the corresponding parts. It is obvious that it is unnecessary that both the rotor and stator electrodes be embossed below the surface. In fact, the rotor may consist of a metal plate which rides on the surface 9 of the stator and has precisely the same eifect insofar as adjustment of capacity is concerned. It is necessary to make the plate 25 of slightly greater diameter than the electrodes 20 and 21 so that it will always ride on the upper surface 9 of the stator. The fiat plate 25 of course should have sufficient rigidity so that it will maintain an accurate spacing between it and the stator electrodes 20 and 21. The metal plate 25 illustrated in Fig. 8 is equivalent to a rotor construction in which the electrode 10 is not embossed below the lower surface 8 of the rotor but rather is flush with that surface. So long as one of either the stator electrodes or the rotor electrodes is embossed below the surface of the corresponding part, a variable capacitor of controlled capacity will be obtained. By embossing electrodes below the surface of a rigid member of insulating material very accurate electrode spacing can be obtained so that the resultant capacity is accurately controlled.

In Figs. 9 and lO is shown a stator which when used with the rotor shown in Figs. 2 and 3 provides a tunable resonant circuit. The stator has electrodes 20a, 21a, provided with terminals, leads, 22a, 23a of the same construction as the corresponding parts in the Fig. 6 stator. A slot 24 provides an air gap between the electrodes 20a and 21a reducing the interelectrode capacitance. The electrodes 20a and 21a may be embossed a controlled distance below the upper surface 90 of the stator or may be flush with the surface 9a. The inductive elements are arcuate sections 26 connecting the electrodes 20a and 21a and lying radially within the arcuate rib 7 which fits in the arcuate groove 6 in the rotor and centers the rotor and stator. .When the Fig. 9 stator is assembled with the Fig. 2 rotor in the manner illustrated in Fig. 1

the electrode 10 on the rotor cooperates with the electrodes 20a and 21a on the stator to provide a variable capacity depending upon the degree of overlap of the rotor and stator electrodes. This variable capacity when combined with the arcuate inductance elements 26 provides a resonant circuit. As in the Fig. 1-7 construction, the capacitance between the rotor electrode 10 and the stator electrodes 20a, 21a is accurately controlled by the depth of embossing. While both the rotor and stator electrodes may be embossed below the respective surfaces 8 and 9a it is only necessary that either the rotor or the stator electrodes be embossed.

In Fig. 11 is shown another stator usable with the Fig. 2 and 3 rotor to provide a tunable resonant circuit. The Fig. 11 stator is made of a flat metal plate having electrode sections 20b and 21b provided with terminal leads 22b, 23b of the same configuration as the correspondingly numbered parts in the Fig. 6 stator. The electrodes 20b and 21b are connected by arcuate inductance elements 26b. When the Fig. 11 stator is used with the Fig. 2 ro- 7 with its surface.

4 tor, the stator rides on the surface 8 of. the rotor and the capacitance between the electrodes 20b, 21b and the electrode 10 is determined by the degree of overlap and by the depth of embossing of the rotor electrode 10 below the rotor surface 8. Since the inductance sections 26b are of fixed dimensions, the frequency to which the resonant circuit is tuned is controlled by the variable capacitance between theelectrodes 10, 20b, and'21b.

In Figs. 12 and 13 is shown a fixed capacitor having a base 27 of rigid insulating materialprovided with a plane upper surface 28 and with two spaced electrodes 29 and 30 which are embossed a controlled depth below the surface 28, for example by the technique illustrated in Figs. 4a, 4, and 5. The electrodes 29 and 30 have lead portions 31 and 32. The other electrode of the capacitor comprises a flat metalplate 33 which overlaps both of the electrodes 29 and 30 and has suflicient projection outside these electrodes so as to be firmly supported on the plane surface 28. Since the depth of embossing of the electrodes 29 and 30 can be accurately controlled there is a fixed and accurately controlled spacing between the electrodes 29 and 30 and the electrode 33. This provides an accurate capacitor.

In the constructions illustrated in Figs. 14-23 inclusive a plurality of pairs of rotor and stator elements are ganged together to provide a variable tuning capacitor. By having the rotor and stator elements consist of disks of insulating material with plane surfaces in face to face contact and with the electrodes on at least one of the disks embossed a controlled depth below its plane surface the electrode spacing can be very accurately controlled and can be made much smaller than inconventional variable tuning condensers. This results in a material reduction in the bulk of the variable capacitor and in a lower cost of manufacture.

The stator shown in Figs. 14 and 15 may be made by the techniques illustrated in Figs. 4a, 4 and 5. It comprises a flat disk 34 of cured plastic impregnated fiber having a plane surface 35 below which is embossed an electrode 36 adhesively joined or united to the disk. The surface 35 is plane and is formed when the unembossed portion of the foil forming the electrode 36 is cut or abraded away as illustrated in Fig. 5. obvious that the electrode 36 may be previously stamped out and embossed below the surface 34 during the molding operation in which case there will be no need'to grind away the unembossed portion of the metal. The disk 34 has ears 37 and 38 provided with holes 39 and 40 for receiving the usual mounting posts 41 and 42. The electrode has a lead portion 43 which extends around the holes 40 and is electrically connected to the mounting post 42 so that all of the stator electrodes 35 are connected in parallel when the stator elements are stacked to form the variable condenser as illustrated in Fig. 1

The rotor illustrated in Figs. 16 and 17 comprises a circular disk 44 of plastic impregnated fiber having a plane surface 45 below which is embossed an electrode 46. At the center of the disk 44 is an opening 4'7 provided with a key-way 48 for mechanically connecting the rotor elements to a shaft 49. There will be electrical connections between the electrodes 4'6 and the shaft 4-9 so that all of the rotor electrodes will be connected in parallel. A plurality of expedients are available for making the electrode connections and these connections are sowell understood that illustration is not required.

When the rotor and stator elements are stacked or ganged together as illustrated in Fig. 18 the plane surfaces 45 of the rotor elements ride on the plane surfaces 35 of the stator elements thereby determining the spacing between the stator and the rotor electrodes 36 and 46. It should be obvious that only one of these electrodes needs be embossed below the surface and the other can be flush section 50 surrounding the periphery of the electrode 36 and the rotor'has a correspondingarcuate section 51 stiri It should be The stator surface 35 has an arcuate:

rounding the periphery of the rotor electrode 46. The arcuate sections 50 and 51 are in the same plane as the surfaces 35 and 45 and are for the purpose of insuring the accurate spacing of the electrodes 36 and 46 in any angular position of the rotor elements. Because the depth of embossing of the rotor or stator electrodes 46 or 36 can be very accurately controlled with respect to the surfaces 45 and 35 the electrode spacing can be made smaller than in conventional constructions and a larger capacity can be obtained in a smaller space.

Although electrodes are illustrated on only one face of the rotor and stator elements, it should be obvious that rotor elements may be provided on both faces of these elements thereby doubling the capacity.

The stator element illustrated in Figs. 19 and 20 comprises a disk of cured plastic impregnated fiber 52 having a plane surface 53 on one side below which are electrodes 54 and 55 adhesively united to the disk and embossed a controlled distance below the surface 53. The disk has ears 56 and 57 provided with holes 58 and 59 for receiving the usual mounting posts. The electrode 54 has an extension 60 surrounding the hole 53 for making electrical connection to the post extending through the hole. The electrode 55 has a similar extension 61 surrounding the hole 59 and likewise serving to make electrical connection to the post extending through the hole.

The rotor illustrated in Figs. 21 and 22 comprises a disk 62 of cured plastic impregnated fiber having a plane surface 63 below which is embossed an electrode 64. The disk has slots 65 for minimizing interelectrode capacity. At the center of the disk is a hole 66 provided with a keyway 67 for making a connection to a center shaft 68. In this construction, there is no electrical connection between the rotor electrode 64 and the center shaft 68 but the capacitor terminals are on the respective stator electrodes 54 and 55.

When the pairs of rotors and stators are stacked as illustrated in Fig. 23 there is provided a variable tuning condenser in which the stator and electrode spacing is accurately controlled by the depth of embossing of the electrodes below plane surfaces on the stacked disks.

6 The plane surfaces on the stacked disks engage at all angular positions of the rotor and accurately maintain the electrode spacing which can be much closer than in the conventional tuning condensers.

What is claimed as new is:

A capacitor having a pair of members with opposed plane surfaces on the respective members in face to face engagement and with opposed electrodes on the respective members having adjacent opposed surfaces of the electrodes separated by an air gap determined from said plane surfaces as a datum plane, one of the members being of molded plastic insulating material and its electrode being metal foil molded in place and occupying part of the surface of said one member and having an adhesive between its inner face and said one member and having its entire outer or exposed face depressed a controlled distance into said one member and having its inner face united by the adhesive to the underlying part of said one member, said underlying part of said one member and the adhesive being molded to conform to the inner surface of the foil, whereby the position of the outer face of the electrode with respect to the plane surface of said one member is located from said plane surface independent of variations in the thickness or distribution of the metal, adhesive or insulating material.

References Cited in the file of this patent UNITED STATES PATENTS 1,603,041 Gaudio Oct. 12, 1926 1,630,885 Barnhart May 31, 1927 1,773,377 Roberts Aug. 19, 1930 2,109,266 Franklin Feb. 22, 1938 2,370,722 Ehlers Mar. 6, 1945 2,427,144 Jansen Sept. 9, 1947 2,438,592 White Mar. 30, 1948 2,492,748 Hibberd Dec. 27, 1949 2,541,749 De Lange Feb. 13, 1951 FOREIGN PATENTS 918,056 France Oct. 7, 1946 

